I need an information about how many natural rivers were altered by removing natural menaders and similar actions excluding dam reservoirs.
Paper by Dr. Stanley Trimble discussed this in the piedmont of SC, USA. Many of the modifications were made to remove blockages for water transport and moving of logs by water, even creating splash dams to contain logs, then break dam during storm to flush downstream such as Chattooga River in NW SC, USA. We have found that LiDAR helps to show some of this past detail of moving the channel against one slope of the valley to maximize area for farming, drainage of wetlands or channelizing and straightening channel systems through communities or urban areas. Some of this channel entrenchment and increased gradient due to channelization or in some instances levees were done to flush sediment and reduce flooding in one area, but often contributing problems to other areas, or the protected areas that become unprotected when measures fail. Modifications to stream and river systems was almost a standard practice of many early engineers, developers, landowners, and farmers who were dissatisfied with the natural channel system and also the meandering in low gradient valleys, before increased understanding of river morphology, behavior, function, dependent aquatic resources, etc. suggest these practices have repercussions. Some loss in meandering systems may also be due to removal of supportive channel vegetation that is critical to maintain meandering bends through through flood stages. The loss of vegetation may in some instances be forests, or in other instances removal of rushes and sedges through disturbance of wet meadows, and the result in valley flooding is the avulsion of the channel through gully development through some meanders. Some channel relocation is normal in braided systems due to channel filling with sediment and relocation. Many regulated changes by straightening of rivers through engineered dredging, etc. may be recognizable from aerial photos, unless constrained by geology such as shear lineament. LiDAR really especially helpful in heavily forested areas, where ground and channel features are obscured.
Most geomorphologists are likely to concentrate on specific areas or basins, even watershed scale in some instances. I dont know of any that have tried to address over multiple country boundaries, this such as for Europe. It seems that over the last few decades, the flooding in some areas such as within the Mississippi River Basin has just become more extreme, and the regulations of the past are locally failing, causing some increased flooding issues. Some of this might be assigned to very severe storm (even climate change), some might be inadequate maintenance of past dredging or leveed systems, dam failures, etc. Since the loss of meandering can be through regulation, management, land use change or more natural channel adjustments through time, the subject could be complex in trying to pin down at the scale suggested. In the USA, the Corps of Engineers may have a few reports on subjects as regulation activities within the Mississippi River System. But it is doubtful that they would include small activities in the headwaters and smaller non-navigable waters accomplished by landowners through time.
William F. Hansen Thanks a lot. Yes it was in general common practice, and lidar or even classical aerial photos may be useful to assess the amount of such alterations. Anyway, no such global analysis is familiar to me and that is why I'am asking. Good subject for some major report but it seems there is no such assessment. I need it for popular conservation education and simply to cite in the introduction of paper devoted to biodiversity and regulation. Thanks!
- Badges
- Science topic
- Similar topics
- Geoscience
- Atmospheric Sciences
- Climate Science
- Climate Change